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flow_dissector: fix clamping of BPF flow_keys for non-zero nhoff 

Don't allow BPF program to set flow_keys->nhoff to less than initial
value. We currently don't read the value afterwards in anything but
the tests, but it's still a good practice to return consistent
values to the test programs.

Signed-off-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
This commit is contained in:
Stanislav Fomichev 2019-04-01 13:57:32 -07:00 committed by Daniel Borkmann
parent 822fe61795
commit b9e9c8599f
1 changed files with 2 additions and 1 deletions
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3
net/core/flow_dissector.c
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@ -717,7 +717,8 @@ bool __skb_flow_bpf_dissect(struct bpf_prog *prog,
/* Restore state */
memcpy(cb, &cb_saved, sizeof(cb_saved));
flow_keys->nhoff = clamp_t(u16, flow_keys->nhoff, 0, skb->len);
flow_keys->nhoff = clamp_t(u16, flow_keys->nhoff,
skb_network_offset(skb), skb->len);
flow_keys->thoff = clamp_t(u16, flow_keys->thoff,
flow_keys->nhoff, skb->len);